RNA is ribonucleic acid. It is a polymer of nucleotides, each made up of:a pentose sugar called riboseone of four bases adenine, guanine, cytosine and uracila phosphate groupThere are three types of RNA: mRNA, tRNA and ribosomal RNA or rRNA.Like DNA it has a sugar-phosphate backbone made of ribose and phosphate groups linked together by phosphodiester bonds.Thymine in DNA is replaced by uracil in RNA.